Whole blood and blood products, such as plasma and serum, have oxidation-reduction potentials (ORP). Clinically the ORP of blood, plasma and serum provides a diagnostic assay of the oxidative status of an animal. More particularly, researchers have determined that the ORP of blood, plasma and serum is related to health and disease.
An oxidation-reduction system, or redox system, involves the transfer of electrons from a reductant to an oxidant according to the following equation:oxidant+ne−⇄reductant  (1)where ne− equals the number of electrons transferred. At equilibrium, the redox potential (E), or oxidation-reduction potential (ORP), is calculated according to the Nernst-Peters equation:E(ORP)=Eo−RT/nF ln [reductant]/[oxidant]  (2)where R (gas constant), T (temperature in degrees Kelvin) and F (Faraday constant) are constants. Eo is the standard potential of a redox system measured with respect to a hydrogen electrode, which is arbitrarily assigned an Eo of 0 volts, and n is the number of electrons transferred. Therefore, ORP is dependent on the total concentrations of reductants and oxidants, and ORP is an integrated measure of the balance between total oxidants and reductants in a particular system. As such, ORP provides a measure of the overall oxidative status of a body fluid or tissue of a patient.
An ORP measurement which is significantly higher than that of normals will indicate the presence of oxidative stress. The presence of oxidative stress has been related to many diseases, and it has been found to occur in all types of critical illnesses. Accordingly, an ORP level significantly higher than that of healthy individuals indicates the presence of a disease and perhaps a critical illness. An ORP measurement which is the same as or lower than that of healthy individuals indicates the absence of oxidative stress and the absence of a disease or critical illness although an overly low number could indicate a problem as well. Thus, the ORP level of a patient can be used by a medical doctor or veterinarian as an aid in diagnosing or ruling out the presence of a disease, particularly a serious illness. Sequential measurements of ORP over time can be used to monitor the progression of a disease and the effectiveness or lack of effectiveness of treatment of the disease. If a patient's ORP does not decrease after treatment, or especially if it increases despite treatment, this may indicate a poor prognosis and the need for more aggressive and/or additional and/or different treatments. In the case of a measurement made by a patient, such as a patient experiencing symptoms of myocardial infarction, the ORP level may indicate the need for the patient to see a doctor or to immediately proceed to an emergency room for treatment.
Oxidative stress is caused by a higher production of reactive oxygen and reactive nitrogen species or a decrease in endogenous protective antioxidant capacity. Oxidative stress has been related to various diseases and aging, and it has been found to occur in all types of critical illnesses. See, e.g., Veglia et al., Biomarkers, 11(6): 562-573 (2006); Roth et al., Current Opinion in Clinical Nutrition and Metabolic Care, 7:161-168 (2004); U.S. Pat. No. 5,290,519 and U.S. Patent Publication No. 2005/0142613. Several investigations have shown a close association between the oxidative status of a critically ill patient and the patient's outcome. See Roth et al., Current Opinion in Clinical Nutrition and Metabolic Care, 7:161-168 (2004).
Oxidative stress in patients has been evaluated by measuring various individual markers. See, e.g., Veglia et al., Biomarkers, 11(6): 562-573 (2006); Roth et al., Current Opinion in Clinical Nutrition and Metabolic Care, 7:161-168 (2004); U.S. Pat. No. 5,290,519 and U.S. Patent Publication No. 2005/0142613. However, such measurements are often unreliable and provide conflicting and variable measurements of the oxidative status of a patient. See Veglia et al., Biomarkers, 11(6): 562-573 (2006); Roth et al., Current Opinion in Clinical Nutrition and Metabolic Care, 7:161-168 (2004). The measurement of multiple markers which are then used to provide a score or other assessment of the overall oxidative status of a patient has been developed to overcome the problems of using measurements of single markers. See Veglia et al., Biomarkers, 11(6): 562-573 (2006); Roth et al., Current Opinion in Clinical Nutrition and Metabolic Care, 7:161-168 (2004). Although such approaches are more reliable and sensitive than measurements of a single marker, they are complex and time consuming. Thus, there is a need for a simpler and faster method for reliably measuring the overall oxidative status of a patient.
The oxidation/reduction potential can be measured electrochemically. Electrochemical devices for measuring ORP of blood and blood products typically require large sample volumes (that is, ten to hundreds of milliliters) and long equilibrium periods. Furthermore, the electrochemical devices have large, bulky electrodes that require cleaning between sample measurements. Such electrochemical devices are poorly suited for routine clinical diagnostic testing. It has been suggested to use electrodes that have undergone treatment to prevent biofouling of the electrode surface. However, such devices necessarily involve complex manufacturing techniques. Moreover, conventional electrochemical devices have not provided a format that is convenient for use in a clinical setting.
The oxidative and radical characteristics of human blood plasma and its blood components (such as low density lipoproteins, serum albumin, and amino acids) can also be determined from photo chemiluminescence, with and without thermo-initiated free radical generation. A photo chemiluminescent system generally includes a free radical generator and a detector that measures chemiluminometric changes in the presence of an antioxidant. More specifically, the blood plasma sample (or one of its components) containing an amount of antioxidant is contacted and reacted with a known amount of free radicals. The free radicals remaining after contacting the blood plasma sample are determined chemiluminometrically. This type of measurement and detection system is not suitable for rapid, large scale measurements of blood plasma samples in a clinical setting.